IRS Commissioner John Koskinen wrote all of the top tax writers in Congress to warn them that lawmakers must act swiftly to renew expired and expiring tax provisions or risk a delay in the start of the 2015 tax filing season.

He told Senate Finance Committee Chairman Ron Wyden, Sen. Orrin Hatch, the top Republican on the committee, Ho...use Ways and Means Committee Chairman Dave Camp, and Rep. Sander Levin, the top Democrat on the committee, that uncertainty over the future of a bundle of miscellaneous tax breaks creates a major burden for the IRS.

He said the tax writers should decide which breaks to extend and which will expire before the end of November.

"This uncertainty, if it persists into December or later, could force the IRS to postpone the opening of the 2015 filing season and delay the processing of tax refunds for millions of taxpayers," he wrote. "Moreover, if Congress enacts any policy changes to the existing extenders or adds new provision, the IRS could have to reprogram systems and make processing changes."

It is the same warning that the IRS has had to issue on several occasions in recent years. The tax extenders are frequently allowed to expire only to be renewed retroactively at a later date. The Finance Committee passed an extension of the majority of expired and expiring provisions in May but the full Senate has yet to consider that legislation.

Meanwhile, the House has passed a series of permanent extensions of individual extenders. Democrats largely oppose the approach and prefer to see a 1-2 year extension of all of the provisions to allow time for lawmakers to work on tax reform.